activity2.java

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        switch(id) {
            // ...

            // up button
            case android.R.id.home:
                finish();
                overridePendingTransition(R.anim.activity_back_in, R.anim.activity_back_out);
                return true;
        }

        return super.onOptionsItemSelected(item);
    }